1. INTRODUCTION
2. ASTRONOMICAL TRACKING
3. SOLTEC TEAMTRACK®
4. HOW DOES DIFFUSE BOOSTER WORK?
5. SOLTEC DIFFUSE BOOSTER PLUG-IN
6. BENEFITS OF WEATHER FORECAST
7. TÜV RHEINLAND OBSERVES 6.9% MORE ENERGY WITH DIFFUSE BOOSTER
8. DIFFUSE BOOSTER INTEGRATED ON TEAM TRACK® SYSTEM. YEARLY RESULTS
9. TÜV RHEINLAND® INDEPENDENT THIRD PARTY VERIFICATION
10. ECONOMICAL SCENARY
11. CONCLUSIONS
12. BIBLIOGRAPHY
TÜV Rheinland has verified Soltec Diffuse Booster algorithm, whose objective is increasing the production of the PV plant even on cloudy days, meaning, when there is more diffuse than direct irradiance.
The algorithm, which uses both sensors and weather forecasts, moves the trackers to the optimal position that captures the maximum irradiance. In this way, the algorithm increases production of cloudy periods by 5.34% and 6.85%, depending on the latitude.
Diffuse Booster is one of the algorithms that make up the Soltec Team Track® extended package, which aims to make plants smarter so that they can anticipate and orient themselves in the most profitable way.
1. INTRODUCTION
Solar tracking systems can turn Photovoltaic Modules (PV) to positions in which received irradiance is enhanced. Single Axis Tracking Systems (SAT) are traditionally designed to “follow” the sun throughout the day, generating up to 25-30% more energy than fixed structures [1].
However, there are tracking strategies which orient trackers to not sun-oriented angles (other than the “typical“ one) with the aim to maximize available power. This performance is normally associated to specific irradiance conditions in which captured irradiance in a position other than solar tracking is more beneficial.
2. ASTRONOMICAL TRACKING
Solar trackers are traditionally oriented to the sun, regardless of whether direct irradiance exists or not. Such type of tracking is called “astronomical tracking”. The sun position for a site (latitude and longitude) at a specific time is known thanks to astronomical Earth movement models and can be easily known using Solar Position Algorithms (SPA) [2, 3]. Based on this information and using geometric relations, astronomical algorithms determine the tracker rotation angle which optimizes PV module orientation [4].
3. SOLTEC TEAMTRACK®
Those standard tracking algorithms does not avoid shading at low sun-elevation periods. With the aim to prevent tracker shading between solar power plant rows, backtracking techniques are applied. Such techniques are more or less effective depending on their level of sophistication. As described on WhitePaper “6.2% TeamTrack Gain” [5], TeamTrack® backtracking techniques improve generation up to 6.2% for Mediterranean latitudes and regular terrains compared to standard tracking. This is achieved thanks to the collaborative tracker positioning in the early and late hours of the day.
Why should Diffuse Booster be used?
Astronomical tracking strategies keep modules oriented to the sun, thus ensuring that under clear sky conditions (responsible for some 90% of annual PV Energy Yield ), trackers capture maximum irradiance. However, modules also remain oriented towards the sun under cloudy conditions, even if this is not always the best position to maximize power generation.
This concept can be easily explained considering that irradiance received by the module (global) can be decomposed as follows:
- Direct irradiance, which comes straight from the sun rays.
- Diffuse irradiance, which comes from all around as a result of solar ray reflection and refraction on air mass, clouds and other objects.1
Under sunny conditions, direct irradiance flux onto the PV module coming from the sun position is always higher than diffuse irradiance, as shown by the arrows in figure 1.
On the contrary, modules receive no direct irradiance when clouds cover the sun. When solar rays pass through the atmospheric air mass and clouds, the only irradiance reaching photovoltaic modules is diffuse. Under these events, global irradiance is emitted homogeneously throughout the celestial sphere. Since there is no preferred direction, trackers would only maximize energy when they “see” a greater amount of sky, as shown in Figure 2.b.
1Albedo-induced reflected irradiance is considered part of diffuse irradiance collected by modules.
Figure 1: Sunny conditions, SAT in astronomical tracking.
Figure 2: Cloudy conditions. A) SAT in astronomical tracking, b) SAT in Diffuse Booster tracking.
4. HOW DOES DIFFUSE BOOSTER WORK?
To best use this energy, tracking systems have to include diffuse energy optimization functionalities. Figure 3 shows the performance of this function compared to standard astronomical tracking throughout a representative day in which the sky gets cloudy. Early in the day, the sun shines and therefore trackers maintain their orientation. As clouds appear, irradiance on the oriented plane decreases considerably, fluctuating as the sky gets overcast and horizontal plane irradiance exceeds steadily oriented irradiance. The lower graph shows how, throughout this period, the angle of the tracker in astronomical tracking remains oriented to the sun position (as shown in Figure 2.a), whereas the tracker with Diffuse Booster active remains horizontal to optimize energy and capture all celestial sphere irradiance (as shown in Figure 2.b). Energy collected by the tracker in optimization mode exceeds in 94 Wh/m2 the astronomical mode one, achieving a daily generation improvement of 1.4%.
Figure 3. Example of Diffuse Booster functionality activation in a representative day with a cloudy afternoon. Spain, March 20th, 2016.
Figure 4 shows this comparison for an example of fully cloudy day. Tracking with active Diffuse Booster increases captured irradiance by 54 Wh/m2, improving full-day power generation in 12.4 %, offering instantaneous improvement peaks of up to 29%.
Figure 4 Diffuse Booster active during a fully cloudy day. Spain, January 3rd, 2016. a) Collected Energy comparison, b) Instantaneous Energy Gain vs astronomical sun-oriented tracking.
5. SOLTEC DIFFUSE BOOSTER PLUG-IN
To achieve production improvements associated to diffuse irradiance optimization, tracking systems require local weather data which can be obtained via forecasts and sensors. Furthermore, determining the exact return-to-tracking time is one of the main challenges for these systems.
Figure 5 shows Soltec Diffuse Booster system performance when the day clears, and the sun comes out. As can be seen, energy levels during periods when the sun shines are five-fold those of fully cloudy event. Such energy gain needs to be utilized. Systems which position trackers based solely on sensor data will return to tracking position when sensors detect increased direct irradiance. Since these systems cannot predict conditions, energy (direct irradiance) is partly wasted while returning to the sun-oriented tracking position. To ensure efficiency of this functionality, it is necessary for systems to predict the return-to-tracking mode, orienting trackers before the first sun’s rays appear. Similarly, a reliable system should ensure trackers are not moved to a diffuse irradiance optimization position in case of one-off fluctuations, which are not sustained in time and are therefore irrelevant in terms of production maximization, thus preventing unnecessary tracker movements.
This anticipation criterion is based on the same concept that fruit ripening schedule: the later they are picked from the tree, the tastier they’ll be, but waiting too many results on fruit falling to the ground. A failed movement of the trackers attempting to improve means lost everything. Systems based solely on the use of sensors wait for fruit to fall to the ground. On the contrary, within the weather forecast inclusion, Soltec Diffuse Booster is activated by double-check information, just the accurate shot.
FIGURE 5: Example of Diffuse Booster in a day with a cloudy morning. Spain, June 5th, 2016.
6. BENEFITS OF WEATHER FORECAST
Soltec’s diffuse irradiance optimization system overcomes all these drawbacks by using weather forecasts in their evaluation.
The Diffuse Booster algorithm developed by Soltec performs a joint analysis of weather forecasts and plant data. Using this methodology to shorten the forecast confidence interval, together with periodic validation based on real-time sensor measurements, favors reliable anticipation of system response.
The use of weather forecasts in Soltec’s Diffuse Booster system makes it possible to confirm that horizontal irradiance exceeds tilted plane irradiance, as well as to confidently anticipate that such conditions will remain over all the cloud events. Similarly, the algorithm also anticipates that, before optimal diffuse maximization conditions cease to exist, the system will orient towards the sun, thus avoiding energy waste (an issue that affects systems based solely on the use of sensors).
To do that, representative sensors strategically distributed throughout the solar plant are used, taking into account aspects such as terrain irregularities and specificities of large solar farms. This distribution is also a redundant system which, by means of joint, synchronized interpretation, increases system reliability.
The use of Diffuse Booster in Team Track® tracking increases power generation up to 12.4% under cloudy days.
7. TÜV RHEINLAND OBSERVES 6.9% MORE ENERGY WITH DIFFUSE BOOSTER
Using the Diffuse Booster system increases annual power generation during cloudy periods. TÜV Rheinland has studied the integration of the Soltec Diffuse Booster algorithm into TeamTrack® system, over the European and Brazilian sites covered on White Paper “6.2% TeamTrack Gain” [5].
Table 1 includes the results of the analysis performed by TÜV Rheinland under TMY2 climate conditions. Results show that Energy Yield increases around 5.3% during the Diffuse Booster activation in Mediterranean and Equatorial climates, reaching a 6.9% gain at Northern latitudes. The Diffuse Booster algorithm optimizes the performance during cloudy days, when power generation increases up to 12.4% for a single day.
2Typical Meteorological Year (TMY), using meteorological data with hourly values in a year for a given geographical location over 2001-2020, generated according to ISO 15927-4. [6]
| 2001-2020 TMY CLIMATE | Mediterranean | Equatorial | Northern |
| Region | Spain | Brazil | Germany |
| Latitude | 41.01 | -6.87 | 52.55 |
| Year Global Horizontal Irradiation (kWh/m2) | 1700 | 1900 | 1000 |
| Year Diffuse Horizontal Irradiation (%) | 36 % | 36 % | 54 % |
| ACTIVATION PERIOD | |||
| Days per year | 87 | 70 | 192 |
| Hours per year | 342 | 231 | 1041 |
| Team Track Energy Yield on cloudy events (kWh/kWp) | 40.17 | 36.95 | 116.96 |
| Diffuse Booster Energy Yield on cloudy events (kWh/kWp) | 42.32 | 38.92 | 124.98 |
| Diffuse Booster Gain on Cloudy Periods | 5.3 % | 5.4 % | 6.9 % |
| BEST DAY | Oct 20th | Dec 17th | Jan 6th |
| % Daily Gain | 12.39 % | 6.28 % | 12.39 % |
TABLE 1: Results of Diffuse Booster activation period over TMY 2001-2020
The study carried out by TÜV Rheinland concludes that Diffuse Booster activation period increments Team Track® Energy Yield by 5.3 % for Mediterranean and Brazilian sites.
8. DIFFUSE BOOSTER INTEGRATED ON TEAM TRACK® SYSTEM. YEARLY RESULTS
The impact of Diffuse Booster on annual generation is linked to the number of cloudy hours and, therefore, to specific site weather conditions. It is worth noting that activation hours in Northern latitudes are five-fold those of Mediterranean conditions. Table 2 shows the comparative extra-gains obtained when Diffuse Booster actuation is added to TeamTrack® over the year, in comparison with basic Team Track and Standard Tracking results previously presented in [5].
9. TÜV RHEINLAND® INDEPENDENT THIRD PARTY VERIFICATION
TÜV Rheinland®, leading technical service organization worldwide, drafted an independent third-party report to assess Soltec’s TeamTrack® algorithm effectiveness.
| Mediterranean Region | Northern Latitude | Equatorial | |||||||
| Team Track® basic Gain Vs. STDT | Diffuse Boster Gain Vs. Team Track® | Composed Gain VS STDT | Team Track® basic Gain Vs. STDT | Diffuse Boster Gain Vs. Team Track® | Composed Gain VS STDT | Team Track® basic Gain Vs. STDT | Diffuse Boster Gain Vs. Team Track® | Composed Gain VS STDT | |
| Yearly Gain | 6.21% | 0.12% | 6.33% | 7.50% | 0.72% | 8.27% | 3.90% | 0.09% | 4.00% |
| Jan | 8.73% | 0.31% | 9.04% | 12.70% | 1.15% | 14.00% | 4.30% | 0.18% | 4.49% |
| Feb | 8.10% | 0.19% | 8.29% | 10.80% | 0.97% | 11.87% | 4.30% | 0.26% | 4.57% |
| Mar | 6.70% | 0.15% | 6.85% | 9.20% | 0.88% | 10.16% | 4.20% | 0.30% | 4.51% |
| Apr | 6.16% | 0.18% | 6.34% | 7.50% | 0.72% | 8.27% | 4.10% | 0.19% | 4.30% |
| May | 4.83% | 0.15% | 4.98% | 5.70% | 0.73% | 6.47% | 3.60% | 0.05% | 3.65% |
| Jun | 4.56% | 0.06% | 4.62% | 4.70% | 0.54% | 5.27% | 3.40% | 0.08% | 3.48% |
| Jul | 4.91% | 0.04% | 4.95% | 5.50% | 0.51% | 6.04% | 3.30% | 0.03% | 3.33% |
| Aug | 5.27% | 0.04% | 5.31% | 6.60% | 0.54% | 7.18% | 3.80% | 0.00% | 3.80% |
| Sep | 6.88% | 0.09% | 6.97% | 9.00% | 0.73% | 9.80% | 4.30% | 0.00% | 4.30% |
| Oct | 7.88% | 0.11% | 7.99% | 10.20% | 1.08% | 11.39% | 3.70% | 0.00% | 3.70% |
| Nov | 8.80% | 0.20% | 9.00% | 13.50% | 1.74% | 15.47% | 3.90% | 0.09% | 3.99% |
| Dec | 9.50% | 0.20% | 9.73% | 13.50% | 0.79% | 14.40% | 3.60% | 0.79% | 4.42% |
TABLE 2: Diffuse Booster monthly Gain in comparison with TeamTrack® and Standard Tracking (STDT) studied in3 [5].
3Diffuse Booster Total Gains composed with Team Track basic vs STDT for regular terrain. Diffuse Booster with 2001-2020 TMY climate. Team Track basic with 2005-2016 TMY climate
Figure 7. Energy Gain monthly distriubtion analized by TÜV Rheinland at sites: Mediterranean (Spain, Castille); Equatorial (Brazil , Picos); Northern (Germany, Hannover)
Table 2 compares the energy yield obtained with Team Track® and Diffuse Booster versus the energy yield obtained with Standard Tracking, defined in [5]. As can be seen, the energy gain obtained from Diffuse Booster is distributed throughout the months, being more intense during the rainy season in each climate pattern, as seen in the figure 7.
Yearly results show that Diffuse Booster may add a 0.12% gain over the 6.2% obtained by Team Track® in Mediterranean latitudes. On the other hand, in Equatorial climates, the Team Track® gain of 3.9% rises to 4.0%, and in Northern latitudes, Team Track® with Diffuse Booster increases energy yield to 8.3% over the standard Tracking.
As summarized in table 3, Soltec’s tracking system with Diffuse Booster gains in comparison with Standard Backtracking are 2.5%, 1.3% and 3.8% for Mediterranean, Equatorial and Northern latitudes, respectively. The following graph illustrates those gains.
| Yearly Energy Yield Gains | Mediterranean Region | Northern Latitude | Equatorial | |||
| TeamTrack® basic | Team Track® & Diffuse Booster | TeamTrack® basic | Team Track® & Diffuse Booster | TeamTrack® basic | Team Track® & Diffuse Booster | |
| VS STD Tracking | 6.2% | 6.3% | 7.5% | 8.3% | 3.9% | 4.0% |
| VS STD Backtracking | 2.3% | 2.5% | 3.1% | 3.8% | 1.2% | 1.3% |
Table 3: Team Track & Diffuse Booster Yearly Gain in comparison with TeamTrack® and Standard algorithms studied in [5].
Figure 8: Team Track® Yearly Gain in comparison with Standard Team Track and Standard Backtracking for Mediterranean case4.
4Diffuse Booster Total Gains composed with Team Track basic vs STDT for regular terrain. Diffuse Booster with 2001-2020 TMY climate. Team Track basic with 2005-2016 TMY climate
As a result of the Diffuse Booster contribution to TeamTrack®, Soltec’s tracking system offers an annual power generation gain of 6.3% vs a Standard Tracking, and 2.5% vs a Standard Backtracking, for Mediterranean latitudes and regular terrains.
10. ECONOMICAL SCENARY
Based on the energy yield results of the TÜV study, Soltec has carried out an economic simulation to illustrate how TeamTrack® (Basic Team Track and Diffuse Booster) contributes to increasing the income of a 100 MWp PV plant.
Table 4 shows this impact in each studied country.
| TeamTrack® | ||||
| Units | SPN | BRL5 | GER | |
| Diffuse Opt. Increase | (%) | 2.5% | 1.3% | 3.8% |
| Energy Price (2) | $/MWh | $38.4 | $36.0 | $58.6 |
| Energy Yield | kWh/kWp | 1,929 | 1,846 | 1,089 |
| MWh/yr-1 | 192,900 | 184,600 | 108,900 | |
| Revenue | $/yr-1 | $7,407,360 | $6,645,600 | $6,377,184 |
| WACC | (%) | 7% | 10% | 5% |
| Revenue over plant-life | $ USD | $88,439,459 | $60,652,864 | $66,983,872 |
| Diffuse Booster + TeamTrack INCOME | $ USD | $2,140,235 | $782,422 | $2,572,181 |
| $/MWp | $21,402 | $7,824 | $25,722 | |
Table 5: Economic impact resulting from the implementation of Team Track® in a 100MWp PV plant. 30 Years Plant Life.
Thus, considering different climates and energy prices, the implementation of TeamTrack® in a 100 MWp PV plant adds to yearly revenues $2 140 235 and $782 422 revenue increase, for Spain and Brazilian regions, respectively. In Northern latitudes, this revenue rises to $2 572 181.
In the light of these results, the appeal of the Diffuse Booster system applies to climates with many cloudy days and to tropical climates or microclimates with recurrent cloud formation at certain times of the day. That means, for example, that correct identification of typical morning clouds in coastal areas or rain season in equatorial regions could lead to significant advantages. Thus, it is relevant to assess the effectiveness of this kind of SAT algorithms with the local weather data of each project. In this sense, PVSyst® features, as of version V7.1, an option to simulate these effects by selecting diffuse energy optimization option.
Year-On-Year Performance
Diffuse booster system energy gain depends on specific weather conditions throughout the year. TÜV Rheinland has also analyzed the behavior of the Spanish site plant for the year 2010. These results, shown in table 6, reflects that the contribution of Diffuse Booster this year increment a 66% the TMY case.
| TMY Energy Yield [kWh/kWp] | Diffuse Booster | Gain | |||
| Period | TeamTrack | & Diffuse Booster | Activation Days | Year | Activation Days |
| TMY | 1784 | 1786 | 87 | 0.12% | 0.82% |
| 2010 | 1743 | 1747 | 102 | 0.20% | 1.31% |
Table 6: Team Track® yearly gain over year 2010 in comparison to TMY
The algorithm extracts more energy from the PV plant during cloudy events, that is, when energy yield is lower. A year with a significant number of these events may significate a lower year energy yield than the TMY case. In addition to increase the incomes during regular-irradiance years, Diffuse Booster is also a powerful tool that helps to palliate an eventual low-irradiance-year mis-generation, that has a deep impact in economics simulation.
Figure 9 Diffuse Booster minimizes the risk of low-irradiance years
5Assumed FX of 5.00 BRLUSD and 1.2 EURUSD and Price from last update (Dec 21, 2020) [7]
11. CONCLUSIONS
Diffuse Booster extracts more energy from PV plant during diffuse irradiance conditions, such as cloudy events.
TÜV Rheinland has observed that activation of Diffuse Booster algorithm increment energy yield of Basic TeamTrack by 5.3% at Mediterranean and Equatorial sites, reaching a 6.9% gain at Northern latitudes. The Diffuse Booster algorithm thus optimizes the performance during fully cloudy days, with power generation increases of up to 12.4% for a single day.
The implementation of TeamTrack®, including Basic Team Track and Diffuse Booster algorithms may raise the year energy yield up to 6.3% in Mediterranean regions, 4.0% in equatorial sites and 8.3% in Northern latitudes. The expected gains in these regions but compared to standard backtracking (default option of PVSyst) are 2.5%, 1.3% and 3.8%, respectively.
Considering different climates and energy prices, the implementation of TeamTrack® in a 100 MWp PV plant adds to yearly revenues $2 140 235 and $782 422 revenue increase, for Spain and Brazilian regions, respectively. In Northern latitudes, this revenue rises to $2 572 181.
Diffuse Booster extra energy may be 66% higher in low-irradiance years compared to TMY, it increases the incomes during regular-irradiance years, and palliates mis-generation of low-irradiance-years.
12. BIBLIOGRAPHY
[1] Posannapeta Y, Gangaram. (2015). Achieve 50% More Energy per Day by Using Solar Tracking Systems. Energetica India (Magazine). 62. Online:
https://www.researchgate.net/publication/320146967_Achieve_50_More_Energy_per_Day_by_Using_Solar_Tracking_Systems
[2] Reda, Ibrahim; Andreas, Afshin, SPA: Solar Position Algorithm, Astrophysics Source Code Library, record ascl:1504.002, April 2015, Bibcode: 2015ascl.soft04002R.
https://www.nrel.gov/docs/fy08osti/34302.pdf
Link tool: https://midcdmz.nrel.gov/solpos/spa.html
[3] A. A. Rizvi, K. Addoweesh, A. El-Leathy and H. Al-Ansary, “Sun position algorithm for sun tracking applications,” IECON 2014 – 40th Annual Conference of the IEEE Industrial Electronics Society, Dallas, TX, 2014, pp. 5595-5598, doi: 10.1109/IECON.2014.7049356.
https://ieeexplore.ieee.org/document/7049356/authors#authors
[4] Marion, W. F., and Dobos, A. P. Rotation Angle for the Optimum Tracking of One-Axis Trackers. NREL 2013. Web. doi:10.2172/1089596.
https://www.nrel.gov/docs/fy13osti/58891.pdf
[5] M. Herz et all. White Paper 6.2% TeamTrack Gain, Soltec lab, December 2020. Online:
https://lab.soltec.com/6-2-teamtrack-gain/
[6] TMY generator, EU SCIENCE HUB ,The European Commission’s science and knowledge service online.
https://ec.europa.eu/jrc/en/PVGIS/tools/tmy
[7] R. Diermann La subasta de Alemania para grandes plantas concluye con el precio más bajo de 0,0488 /kWh. Pv magazine Alemania, Dec 2020 Online:
https://www.pv-magazine.es/2020/12/21/la-subasta-de-alemania-para-grandes-plantas-concluye-con-el-precio-mas-bajo-de-00488-e-kwh/